U.S. patent application number 10/038459 was filed with the patent office on 2002-12-12 for universal millimeter-wave housing with flexible end launchers.
Invention is credited to Bui, Long Q., Shih, Yi-Chi, Shishido, Tsuneo.
Application Number | 20020186105 10/038459 |
Document ID | / |
Family ID | 23719729 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020186105 |
Kind Code |
A1 |
Shih, Yi-Chi ; et
al. |
December 12, 2002 |
Universal millimeter-wave housing with flexible end launchers
Abstract
A precision non-symmetrical L-shape waveguide end-launching
probe for launching microwave signals in both vertical and
horizontal polarizations is disclosed. The L-shape waveguide probe
is in a form of thin plate, has a first arm and a second arm, and
is precisely fabricated and attached to one end of the central
metal pin of a feedthrough. The feedthrough is installed to an
aperture formed in a major wall of the universal conductive housing
to achieve hermetic sealing. The L-shape waveguide probe is aligned
by means of a specially designed alignment tool so that long axis
of the second arm is always perpendicular to the broad walls of the
output waveguide, which is mounted to the universal housing with
the broad walls of the output waveguide either horizontally or
vertically. Hence, in this invention, an end-launching arrangement
using the L-shape probes that could yield a flexible waveguide
interface either in horizontal polarization or vertical
polarization is provided. The impedance matching and frequency
bandwidth may be adjusted by controlling dimensions and positions
of the L-shape probe. A plurality of the thin plate L-shape
waveguide probes is fabricated by a micro lithography and etching
method to ensure reproducibility and reliability. By incorporating
with an impedance transformation section having a slot, broad band
performance is achieved using the L-shape waveguide probe.
Inventors: |
Shih, Yi-Chi; (Palos Verdes
Estates, CA) ; Bui, Long Q.; (Palos Verdes Estates,
CA) ; Shishido, Tsuneo; (Rancho Verdes Estates,
CA) |
Correspondence
Address: |
Dr. Yi-Chi Shih
2220 Thorley Place
Palos Verdes Estates
CA
90274
US
|
Family ID: |
23719729 |
Appl. No.: |
10/038459 |
Filed: |
January 7, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10038459 |
Jan 7, 2002 |
|
|
|
09433318 |
Nov 3, 1999 |
|
|
|
6363605 |
|
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Current U.S.
Class: |
333/208 ;
333/248; 333/33 |
Current CPC
Class: |
Y10S 29/016 20130101;
Y10T 29/49052 20150115; Y10T 29/49018 20150115; Y10T 29/49016
20150115; Y10T 29/49064 20150115; H01P 11/00 20130101 |
Class at
Publication: |
333/208 ; 333/33;
333/248 |
International
Class: |
H03H 007/38; H01P
001/20 |
Claims
What is claimed is:
1. An end launcher of microwave signals with controlled electric
field polarization for transition between an MMIC and a waveguide
connection, comprising: a universal conductive housing having at
least a broad wall and a major wall, at least one cavity with a
platform defining a reference plane for the accommodating said MMIC
and control components, said reference plane is substantially
parallel to said broad wall, having at least one feedthrough
mounted in said major wall each with one metal pin having a first
end portion and a second end portion; a conductive plate with a
first arm having a first axis, a first length and a first width and
a second arm having a second axis, a second length and a second
width defining a first broad wall and a second broad wall, said
first arm and second arm defining a thickness and forming an
L-shape waveguide probe, one end portion of said first arm having a
slot with a slot width and a slot length for the connection to the
first end portion of said metal pin of the feedthrough in said
universal conductive housing, said L-shape waveguide probe being
aligned so that the second axis is substantially parallel to said
major wall of the universal conductive housing, distance between
the second axis and said major wall being selected on the basis of
frequencies of microwave signals; a conductive universal launching
adapter having a through channel with two long inner walls and two
short inner walls, said two long inner walls and two short inner
walls defining a cross-section of said through channel, said
universal launching adapter being mounted to the major wall of said
universal conductive housing, position of the second arm of said
L-shape waveguide probe is adjusted to be substantially at a
central region of the cross-section of said universal launching
adapter; and a waveguide section with two broad inner walls and two
narrow inner walls, said two broad inner walls and two narrow inner
walls defining a cross-section of said through channel.
2. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1, wherein said first
length, second length, first width and second width of said L-shape
waveguide probe being selected according to operating frequencies
of said microwave signals and characteristic impedance.
3. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1, wherein distance
between said major wall of the universal conductive housing and
said second axis is selected to be substantially equal to a quarter
of wavelength of microwave signals being excited to increase the
launching efficiency.
4. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1, wherein said slot width
is slightly greater than diameter of said metal pin to facilitate
attachment of said L-shape waveguide probe to said metal pin.
5. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1, wherein said second
axis of L-shape waveguide probe being aligned to be parallel to
said major wall of the universal conductive housing and parallel to
said broad wall of the universal conductive housing, the long inner
walls of said through channel being aligned to be perpendicular to
said reference plane or broad wall of the universal conductive
housing and the two broad inner walls of said universal launching
adapter being aligned to be perpendicular to said reference plane
or broad wall of the universal conductive housing, for the
excitation of microwave signals with electric fields substantially
parallel to said reference plane or broad wall of the universal
conductive housing.
6. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1, wherein said second
axis of L-shape waveguide probe being aligned to be parallel to
said major wall of the universal conductive housing and
perpendicular to said broad wall of the universal conductive
housing, the long inner walls of said through channel being aligned
to be parallel to said broad wall and the two broad inner walls of
said universal launching adapter being aligned to be parallel to
said reference plane or broad wall of the universal conductive
housing for the excitation of microwave signals with electric
fields substantially perpendicular to said reference plane or broad
wall of the universal conductive housing.
7. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1 wherein the thickness of
said L-shape waveguide probe is chosen to be in a range from 50
micrometers to 400 micrometers.
8. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1 wherein said L-shape
waveguide probe is fabricated by a micro lithography and etching
method from a conductive sheet, a layer of metal is deposited on
all walls of said L-shape waveguide probe to increase surface
conductivity, said metal for the layer being selected from a group
consisted of gold and silver.
9. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1 wherein alignment of
said L-shape waveguide probe to said metal pin is performed in a
precision alignment jig, said precision alignment jig has one
preformed shallow cavity to accept said L-shape waveguide probe and
a platform to accept said universal conductive housing, said
distance between the second arm and the major wall of said
universal conductive housing being maintained by separation between
an edge of said platform and said shallow cavity, the connection of
said L-shape waveguide probe to said metal pin is achieved by
welding.
10. An end launcher of microwave signals for transition between an
MMIC and a waveguide connection in claim 1 wherein alignment of
said L-shape waveguide probe to said metal pin is performed in a
precision alignment jig, said precision alignment jig has one
preformed shallow cavity to accept said L-shape waveguide probe and
a platform to accept said universal conductive housing, said
distance between the second arm and the major wall of said
universal conductive housing being maintained by separation between
an edge of said platform and said shallow cavity, the connection of
said L-shape waveguide probe to said metal pin is achieved by
soldering.
Description
FILED OF THE INVENTION
[0001] This invention relates generally to a precision
non-symmetrical waveguide probe and a universal impedance
transformation section for launching microwave signals for broad
band applications. More particularly, the invention relates to an
end-launcher with a non-symmetrical waveguide probe for operation
in both vertical and horizontal polarization and with improved
frequency bandwidth.
BACKGROUND OF THE INVENTION
[0002] The recent development of data communications and personal
communication systems (PCS) has led to a drastic increase in the
traffic in RF transmission. In order to meet this increase,
communication systems at millimeter wave frequencies (greater than
25 GHz) are required. The circuits for operation at these high
frequencies are generally fabricated using semiconductors with high
electron mobility, such as GaAs and related compounds, and are
often called Monolithic Microwave Integrated Circuits (MMICs).
These MMICs must be mounted in a housing with other components to
form a complete module. The requirements for an ideal housing
include: [1] universal RF input/output terminals for coaxial and/or
waveguide interfaces, [2] hermetically sealed terminals for DC and
RF, [3] gold plating for thermal compression bonding, [4] proper
cavity design to minimize moding and [5] mounting interface for
heat sink attachment.
[0003] Since the wavelength of a millimeter wave is short, the
requirements for the MMICs fabrication and the tolerance of
alignment and dimensions of parts are critical. Hence, a slight
deviation of the dimensions or position of parts used in the
housing and specifically in connection from the predetermined
values may result in poor performance of the entire module. This is
particularly true for the RF input and output transitions. In
addition to the design and fabrication of MMICs, one of the
critical steps for obtaining a high quality millimeter wave module
is to provide a precise and reproducible RF transition between the
MMICs and connection means attached to the housing.
[0004] The requirements for the RF transition include the
following: [1] a glass bead directly mated with coaxial connectors,
[2] a precisely fabricated probe attached to the bead for proper
impedance matching. A transition between a waveguide and microstrip
line has been reported in "1988 IEEE MTT-S Digest, pp. 473-474"
entitled "Waveguide-to-Microstrip Transitions for Millimeter-Wave
Applications" by Yi-Chi SHIH Thuy-Nhung TON and Long Q. BUI, both
SHIH and BUI are also the common co-inventors of the present
invention. For the method involving waveguide-to-microstrip
transition, dimensions of the microstrip line must be controlled
precisely and aligned to an aperture in the wall of the housing in
order to achieve matched impedance, for example 50 ohms. For
reliable operation, the microstrip line part must be secured to the
aperture of the housing, which often affects the alignment of the
microstrip to the aperture of the housing.
[0005] A millimeter wave waveguide launch transition feedthrough
was also disclosed in U.S. Pat. No. 5,376,901 entitled
"Hermetically Sealed Millimeter Waveguide Launch Transition
Feedthrough" granted to Steven S. Chan, Victor J. Watson, Cheng C.
Yang and Stuart Kam. An electrically conducting pin with a
cylindrical or conical conductive bead head is first formed into a
waveguide probe for the transition feedthrough. The transition
feedthrough is then mounted in an aperture of a housing with the
bead head extending inside an integrated waveguide. Using their
method and structure, it is difficult to obtain positional
reproducibility of the bead head with respect to the integrated
waveguide, especially for applications at millimeter wave
frequencies. This is because there is always a gap between the ring
and inner wall of the aperture in the housing. Hence, the
uniformity of the transition feedthrough in the final modules can
not be guaranteed. In addition, the fabrication of the cylindrical
or conical waveguide probes is relatively expensive due to the
tight requirements in dimensions and position of the central
hole.
[0006] In order to achieve low cost production of millimeter wave
modules, it is preferable to use housings with the same structure
and dimensions for different modules. To achieve this, the housings
should allow RF input and output to be achieved with either coaxial
connector or waveguide connector. The housings should preferably be
capable of hermetic sealing in order to isolate the MMICs and
components from environmental contaminants.
[0007] In U.S. patent application Ser. No. 09/351,362, filed by
Yi-Chi Shih, Long Q. Bui and Tsuneo C. Shishido on Jul. 12. 1999, a
universal conductive housing for different millimeter wave MMICs
with a feedthrough has been disclosed. A plate shape waveguide
probe, which is symmetrical and fabricated by a micro lithography
and etching method, is aligned using a precision alignment tool
with respect to a pin of the feedthrough and welded or soldered by
a miniature solder. The uniformity and reliability of the waveguide
transition has been improved using the structure described in the
U.S. patent application Ser. No. 09/351,362. However, since the
waveguide probes described in that invention are symmetrical and
aligned perpendicular to the major exterior wall of the universal
conductive housing and perpendicular to the broad walls of the
waveguide, the electric field polarization is always perpendicular
to the major exterior wall of the universal conductive housing.
Hence, the input/output waveguide interface always forms a 90
degrees angle with respect to the normal of major walls of the
universal conductive housing. In many applications, it is very
desirable and sometimes necessary to integrate components in-line
with the main housing at the waveguide input/output interfaces,
i.e. the long axis of the input/output waveguide interface should
form a near zero degree angle with respect to the normal of major
walls of the universal housing. This requirement thus creates a
need to have a new arrangement and structure for the waveguide
probe. Furthermore, it is preferable to have a waveguide transition
with operating frequency range broader than the previous structure
involving symmetrical waveguide probes.
SUMMARY OF THE INVENTION
[0008] This invention provides a non-symmetrical waveguide probe
incorporated with a universal adapter to form a microwave
end-launcher. The non-symmetrical waveguide probe is made of a thin
plate, preferably in an L-shape and with an aligning slot along the
central axis of the first arm. A second arm is arranged to be
substantially perpendicular to the first arm in order to obtain
controlled electric field polarization. The L-shape waveguide probe
may be positioned precisely by an alignment jig so that the slot is
aligned to the pin of a feedthrough before welding or soldering. By
aligning the L-shape waveguide probe so that the long axis of the
second arm is perpendicular to the broad walls of the output
waveguide, an end launcher with vertical electric field
polarization, with respect to the main housing reference plane, is
obtained after the welding or soldering.
[0009] The electric field polarization may be changed from
perpendicular to parallel to the main housing reference plane by
rotating the L-shape waveguide probe and universal launcher
adapter. By controlling the dimensions of the L-shape waveguide
probe and the positions in the output waveguide, the central
frequency of operation may be adjusted and the frequency range of
operation of the transition may be increased. Since the L-shape
waveguide probes are preferably manufactured by a micro lithography
and etching method, not only the dimensions of each probe can be
kept to the designed values but also the cost may be reduced.
Furthermore, with the precision alignment method provided in this
invention, the uniformity of characteristics of the waveguide
probes produced among different modules may be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1(a) is a schematic cross-sectional view of the prior
art feedthrough for use with the housing shown in FIG. 1(b). FIG.
1(b) is a schematic top view of a conductive housing for MMICs.
With the prior art waveguide probe (38), electric field
polarization of the microwave signals excited is always
perpendicular to the major exterior wall (28a). FIG. 1(c) is a
prior art symmetrical waveguide probe.
[0011] FIG. 2 is a schematic top view of the L-shape
non-symmetrical waveguide probe with the first arm (41) and the
second arm (42) according to this invention.
[0012] FIG. 3(a) is a schematic view of the conductive housing with
an L-shape waveguide probe (40). Using the L-shape waveguide probes
provided in this invention, microwave signals with electric field
polarizations parallel to the major exterior wall (28a) can be
easily obtained. FIG. 3(b) is a schematic view of a universal
launcher adapter (51') for the excitation of microwave signals with
vertical electric field polarization. FIG. 3(c) is a waveguide
section for receiving and propagation of microwave signals excited
by the L-shape waveguide probe. FIG. 3(d) is a universal launcher
adapter rotated by 90 degrees for the excitation of microwave
signals with horizontal electric field polarization FIG. 3(e) is a
schematic front view of the universal launcher adapter showing a
slot (54a) formed in the through channel for impedance
transformation.
[0013] FIG. 4(a) is a schematic cross-sectional view of the metal
substrate with two photoresist layers coated on the two surfaces
for the fabrication of non-symmetrical L-shape waveguide probes.
FIG. 4(b) is a top view of the first photomask used. FIG. 4(c) is a
cross sectional view of the substrate after etching of the exposed
regions. FIG. 4(d) is a top view of etched waveguide probes
connected by fine brass wires (66, 66b').
[0014] FIG. 5 is a schematic partial view of the conductive housing
(20), L-shape waveguide probe (40) in a precision alignment tool
(80) for aligning and mounting the L-shape waveguide probe to
central metal pin of the feedthrough installed in the conductive
housing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Referring to FIG. 1(a), there is shown according to the
prior art method an RF feedthrough (1) consists of a central metal
pin (2), hereinafter called pin, which is partly enclosed with
glass (3) and a metal ring (4). Diameter (5) and length (6) of
first part (7) of the pin and inner diameter (8) of the metal ring
may be designed according to known prior art method so that when
installed to a conductive housing, the impedance of the RF
feedthrough can be matched with the characteristics impedance of
the MMIC. For instance, a pin with a diameter of 10 mil may be
used. The outer diameter (9) of the metal ring is about 10-20
micrometers smaller than the main diameter (21) of the bores (22)
shown in FIG. 1(b) of a universal conductive housing. Furthermore,
the length (10) of the metal ring (4), or the second length of pin,
is selected to be substantially equal to the major depth (23) of
the bores as shown in FIG. 1(b). The third length (11) of the pin
is selected so that contact attachment or wire bonding can be
easily performed to the MMIC (24).
[0016] FIG. 1(b) shows a universal conductive housing (20)
according to a prior art, hereinafter called housing for an MMIC
(24) and components (25) for control and biasing. The housing is
constructed preferably with conducting materials such as brass or
Al. At least one cavity (26) with a platform (26') is created to
accommodate the MMIC (24). A second cavity (27) may also be created
to accommodate other components (25). Bores (22) with a major depth
(23) are cut through two parallel major walls (28) of the housing,
to accommodate transition RF feedthrough beads (1). The major depth
(23) of the bores is selected so that the RF feedthrough beads (1)
may be used to direct microwave signals from/to the MMIC. Each of
the parallel major walls (28) has one major exterior wall (28a). At
least one DC feedthrough (29) may be installed to bores (30) for
supplying dc power or a control signal to the MMIC.
[0017] To form a waveguide transition according to U.S. patent
application Ser. No. 09/351,362, a plate shape waveguide probe
(38), which is symmetrical with respect to the long axis (37) of
pin, is attached to the end of the first part of the pin (7). As
shown in FIG. 1(c), the waveguide probe (38) according to the
previous invention is symmetrical with respect to the axis (15) of
the slot (16). The symmetrical waveguide probe is characterized by
a major probe wall (30). Although the plate shape waveguide probe
(38) may be fabricated by mechanical machining methods, a micro
lithography and etching method may be preferably used.
[0018] The waveguide probe (38) is aligned and soldered or welded
to the end of the first part (7) of the pin extending outside the
housing, as shown in FIG. 1(b). After this, a section of waveguide
(31), having two broad side walls (32,33) and an end wall (34), is
aligned and mounted to the exterior major wall (28) of the housing
(20). It is noted that a portion of the broad side wall (32) of the
waveguide has been removed whereas the other broad side wall (33)
is intact, so that when the section of waveguide is mounted and
attached to the housing, a complete waveguide cavity (35) is
formed. The end wall (34) of the section of waveguide is adjusted
so that the distance (36) between the end wall (34) and the central
line (37) of the waveguide probe is substantially equal to a
quarter of the wavelength of the microwave signals to be
propagated.
[0019] In most of the prior art methods, cylindrical or conical
beads are used as the waveguide probes in waveguide transition.
These beads are symmetrical and have certain performance limits. In
addition to the higher cost for the fabrication, it is rather
difficult to attach the cylindrically- or conically-shaped beads to
ends of fine metal pins, especially for high frequency
coaxial/waveguide transitions. Since the launching efficiency and
frequency response of a waveguide/coaxial transition are determined
by the shape, dimensions and position of the waveguide probe within
the waveguide, it is more difficult to achieve microwave
transitions using the prior art cylindrical or conical beads. Even
the plate shape waveguide probe disclosed in U.S. patent
application Ser. No. 09/351,362, filed Jul. 12. 1999 is symmetrical
with respect to the central axis. Hence, when the prior art
waveguide probe is mounted to the pin of a feedthrough, the
waveguide probe is always symmetrical with respect to central line
(37).
[0020] During the system integration, it is often necessary to
combine several components or modules at their waveguide
interfaces. For some components, it may be preferable to have the
electric field of microwave signals, which is always perpendicular
to the broad walls of the waveguide, to be parallel to or
perpendicular to a reference plane. In the present description, the
reference plane is taken as the broad walls (20b in FIG. 3(a)) of
the universal conductive housing. Hence, in FIG. 1(b), the
corresponding reference plane is the plane parallel to the top view
plane. The reference plane is shown as the plane defined by a broad
wall (20b) given in FIG. 3(a). It is noted that it is preferable to
fabricate the conductive housing so that the reference plane
defined by the broad wall is substantially parallel to a plane
defined by the MMIC (24). Furthermore, it is preferable to have the
major exterior wall (28a) to be perpendicular to the reference
plane. When the electric field of the microwave signals is parallel
to the reference plane (20b) and major walls (28a in FIG. 3(a)) of
the universal housing, it is normally referred to as the horizontal
polarization. For other components, it may be preferable to have
the electric field perpendicular to the reference plane, which is
referred to as the vertical polarization. As a result, waveguide
twists are often required in the integration using prior art
waveguide probes, which require more volume, weight and cost. Since
the universal launcher adapters in this invention are to serve as
the interface between the universal conductive housing and the
waveguides, it is very desirable to be able to interface microwave
signals from the MMIC with other components in either vertical or
horizontal polarization.
[0021] According to a first embodiment of this invention, a
non-symmetrical waveguide probe (40) as shown in FIG. 2 is provided
to improve the control of polarization and bandwidth. The
non-symmetrical waveguide is very different from the prior art
symmetrical waveguide probe both in geometrical shape and in the
characteristics of electrical excitation. The non-symmetrical
waveguide probe (40) is made of a thin plate of metals or alloys
such as brass or copper. Thickness of the plate for the
non-symmetrical waveguide probes is in the order of 10 mils. The
waveguide probe consists of a first arm (41) and a second arm (42).
The long axis (41a) of the first arm is arranged to be
substantially perpendicular to the long axis (42a) of the second
arm so that they form an L-shape non-symmetrical waveguide probe. A
slot (44) is formed in the central left portion of the first arm.
Width (45) of the slot is slightly greater than the diameter (5) of
pin shown in FIG. 1(a) whereas the length (46) of the slot is less
than the length (6) of the first part on the pin (7). Corner (43)
of the overlapped region between the first arm and the second arm
is rounded whereas left-hand corners (47, 48) of the first arm are
also rounded in order to improve the launching performance of the
microwave signals. The L-shape waveguide probe is also
characterized by a first broad wall (49) and a second broad wall
(not shown) which are parallel to the long axis (41a) and the long
axis (42a).
[0022] Length (41b) of the first arm is selected to be
substantially equal to length (42b) of the second arm whereas width
(41c) of the first arm is selected to be substantially equal to
width (42c) of the second arm. In addition, the length (41b) is
selected to be approximately equal to a quarter of wavelength of
the microwave signals to be excited. It is noted that the relative
dimensions provided above for the non-symmetrical waveguide probe
are given only as an example. Relative dimensions different from
the ones given may be used according to the wavelength range of
operation. Furthermore, the angle between axis (41a) and axis (42a)
may be slightly different from 90 degrees as long as the axis (42a)
can be aligned to be parallel to major exterior wall (28a).
Although the non-symmetrical waveguide probes may be manufactured
by precision mechanical machining, it is preferable to manufacture
them by micro lithography and etching processes. In subsequent part
of the description, a procedure employing micro lithography will be
specifically described.
[0023] To form a microwave end launcher with controlled
polarization and improved frequency bandwidth, the non-symmetrical
waveguide probe (40) is mounted at one end (7) of the pin of a
feedthrough (1), as shown in FIG. 3(a). The feedthrough is mounted
in a major wall (28) of a conductive housing (20). The conductive
housing has two broad walls (20b) and is formed by metals or
alloys. Inside the conductive housing there are MMICs and
components. To facilitate the mounting of a waveguide section (50,
in FIG. 3(c)) for receiving and guiding the microwave signals
excited by the non-symmetrical waveguide probe, a universal
launcher adapter (51, FIG. 3(b)) is provided. The universal
launcher adapter is constructed by metals, alloys or plastic
materials with layers of metals coated on all walls. A through
channel (52) is arranged in the center of the broad wall (53). The
through channel is defined by two long walls (55), defining a
height (55a), and two short walls (54), defining a width (54a).
Both the width (54a) and height (55a) of the through channel are
selected to be the same as that for the inner cavity (58) of the
waveguide section (50) used. By providing a precision slot (54a in
FIG. 3(d)) in one of the two short walls, the universal launcher
adapter also serves as a universal impedance transformation
section. Another universal lunched adapter (51") may also be
connected to the same universal conductive housing.
[0024] There are four screw holes (51a), one in each corner of the
broad wall (53) of the universal launcher adapter. Positions of the
four screw holes (51a) are arranged to match the positions of four
screw holes (50a) in the flange (50b) of the waveguide section (50)
for mounting purpose. There are additional four screw holes (51b,
51b') in the universal launcher adapter (51). Positions of two
(51b) of the four screw holes are arranged to match the positions
of two screw holes (20a) in the major wall (28) of the conductive
housing (20) when mounted in one position. Positions of two other
screw holes (51b') are also arranged to match the positions of the
two screw holes (20a) in the major wall (28) of the conductive
housing (20) when mounted in the other position (see FIG. 3(d).
[0025] When the L-shape waveguide probe (40) is mounted at the end
portion of the first part of the pin (7), which extends outside the
conductive housing (20), with the long axis (42a) of the second arm
substantially perpendicular to the broad walls (20b) of the
conductive housing, defining a reference plane, and with the broad
wall (49, in FIG. 2) of the waveguide probe substantially
perpendicular to the major exterior wall (28a) of the conductive
housing, the electric field polarization of microwave signals
excited by the L-shape waveguide probe will be substantially
perpendicular to the broad walls (20b) of the conductive housing.
As described before, it is preferable to fabricate the conductive
housing so that the reference plane defined by the broad wall of
the conductive housing is substantially parallel to a plane defined
by the MMIC (24). When the universal launcher adapter (51' in FIG.
3(b)) is mounted to the major wall (28) by aligning screw holes
(51b') to screw holes (20a), the polarization of the excited
microwave signals will be perpendicular to the long walls (55) of
the through channel. Hence, when the waveguide section (50) is
mounted to the universal launcher adapter, with the cross-section
of the cavity of the waveguide coinciding the through channel (52),
microwave signals with polarization substantially perpendicular to
the broad walls (56) of the waveguide section can be obtained and
propagated. The electric polarization is now vertical with respect
the broad walls, which are substantially parallel to the reference
plane, of the universal conductive housing.
[0026] Alternately, if the L-shape waveguide probe (40) is rotated
by 90 degrees with respect to the axis of pin (7) so that the
second axis of the second arm is parallel to the broad wall (20b)
and the major exterior wall (28a), the polarization of the excited
microwave signals will be different. To guide the microwave
signals, the universal launcher adapter (51') is also rotated by 90
degrees as shown in FIG. 3(d) to form a new end launcher (51). When
the universal launcher adapter is mounted to the major wall (28),
screw holes (51b) will be aligned to screw holes (20a). The
polarization of the excited microwave signals is still
perpendicular to the long walls (55) of the through channel. Hence,
when the waveguide section (50) is mounted to the universal
launcher adapter, with the cross-section of the cavity of the
waveguide coinciding the through channel (52), microwave signals
with polarization substantially perpendicular to the broad walls
(56) of the waveguide section can be obtained and propagated. The
electric polarization is now horizontal with respect the broad
walls, which are substantially parallel to the reference plane, of
the universal conductive housing. It is noted that, by providing a
precision slot (54a) in one of the two short walls, the universal
launcher adapter also serves as a universal impedance
transformation section.
[0027] In order to achieve high efficiency excitation of microwave
signals, as shown in FIG. 3(a), it is preferable to mount the
L-shape waveguide probe so that the distance (57) between the major
exterior wall (28a) and the long axis (42a) of the second arm is
substantially equal to one quarter of a wavelength of the microwave
signals to be excited and propagated. This can be achieved by
designing the length (41b in FIG. 2) of the first arm to be
slightly than one quarter of the wavelength.
[0028] From the above description, it is evident that microwave
signals with controlled polarization with respect to the reference
plane of the universal conductive housing can be excited and
propagated through a receiving waveguide section using the L-shape
waveguide probe provided in this invention. The universal launcher
adapter may allow the adaptation of a waveguide section easily be
made to the conductive housing in order to receive and propagate
microwave signals with the controlled polarization.
[0029] As stated in the previous paragraph, the length (41b in FIG.
2) of the first arm is selected so that the second arm (42) is
located at a distance (57) from the major exterior wall (28a) of
the main body, as shown in FIG. 3(a). This distance (57) is
approximately a quarter-wavelength of the operating frequency.
Length (42b in FIG. 2) of the second arm is also selected to be
approximately equal to a quarter-wavelength of the operating
frequency so that it has good coupling to the waveguide mode. The
first arm is required for the attachment of the probe to the pin
(7) and provides a proper distance of the second arm from the major
exterior wall (28a). Since the length of the first arm is
approximately equal to a quarter-wavelength of the operating
frequency, it is also used as an impedance transformer to fine
adjust the matching between the waveguide radiation impedance of
the probe and the transmission-line impedance in the conductive
housing. Therefore, the width of the first arm (41 in FIG. 2) is
also selected to provide adequate impedance for matching. As far as
the width of the second arm (42) is concerned, it is chosen just
for providing mechanical strength, for ease of manufacturing and
assembly. More than one end launcher may be connected to the same
universal conductive housing. In FIG. 3(a), (51") represents
another end launcher.
[0030] For those skilled in the art, it is understood that the
dimensions of cross section of the waveguide used are determined by
the frequencies of the microwave signals to propagate. Once the
dimensions of the waveguide section have been determined,
dimensions of the non-symmetrical waveguide probes may be designed.
Dimensions of the non-symmetrical waveguide probes should not be
too large in order to avoid shorting and impedance mismatch. In
order to reduce production cost of the L-shape waveguide probes, it
is preferable to fabricate them by micro lithography and etching
processes. In addition to reduction of cost, the purposes of
employing the micro lithography and etching method to fabricate the
non-symmetrical waveguide probes are [1] to increase the precision
of dimensions and [2] to improve the component reproducibility.
Details of the micro lithography fabrication of the waveguide
probes are given below.
[0031] Referring to FIG. 4(a)-(d), which provide flow diagrams of
main fabrication steps and photo mask patterns, the fabrication of
precision L-shape waveguide probes according to a second embodiment
of this invention is performed as follows. As shown in FIG. 4(a), a
brass substrate (60) with a thickness of about 10 mil is first
solvent cleaned and baked dry. The thickness of the substrate 10
mil is selected to be the same as the diameter of central pin (7 in
FIG. 3(a)) to facilitate the subsequent attachment of the waveguide
probe to the pin. Although the value of 10 mil is given as an
example for the substrate thickness, substrates with thickness
other than 10 mil such as in a range 50 micrometers to 400
micrometers may be used. A first footrests layer (61) of a
thickness about 1-2 micrometers is then applied on the front
surface and a second footrests layer (62) is applied on the back
surface of the brass substrate. After a soft baking at 90.degree.
C. for 10 minutes, the first photoresist layer (61) on the front
surface is exposed to UV light through a first photo mask (63)
while the second photoresist layer on the back surface is
unexposed. It is noted that the purpose of the second photoresist
layer is for protection of the substrate during subsequent etching.
The first photo mask contains opaque regions (64) and transparent
regions (65). These regions are designed so that a plurality of
waveguide probes can be formed on a brass substrate in one
fabrication run. A positive tone photoresist such as AZ-1820 from
Shipley Company, Massachusetts may be used. Since AZ-1820 is a
positive tone photoresist, the opaque regions (64) define the
dimensions and shape of the non-symmetrical waveguide probes.
According to this invention, it is preferred to connect all of the
waveguide probes together electrically to facilitate the
electrodeposition of Au or Ag layer. FIG. 4(b) shows a top view of
the patterns on the first photomask used. To simplify the
explanation, the first photomask provided contains nine
non-symmetrical waveguide probe patterns (40a). Each of the
waveguide probe patterns is connected electrically to adjacent four
waveguide probe patterns by fine wire patterns (66a, 66b). The
purpose of the fine wire patterns is to create fine brass wires
after etching to provide electrical connection, to facilitate the
electrodeposition of Au or Ag. Furthermore, a slot pattern (67a) is
created in each waveguide probe pattern (40a). Hence after etching,
a slot (67 in FIG. 4(e)) will be created in each non-symmetrical
waveguide probe. This slot will allow the attachment of a waveguide
probe to the end of the first part of pin (7) of the feedthrough as
shown in FIG. 3(a). It is noted that the width (77a) of the slot
pattern (67a) is selected so that after etching, the width (77 in
FIG. 4(d)) of slot in the formed waveguide probe is slightly
greater than the diameter of the pin (7) shown in FIG. 3(a).
[0032] After development of the photoresist on the front surface,
the patterns on the first photomask shown in FIG. 4(b) is
transferred onto the first photoresist layer with exposed brass
regions and unexposed brass regions. The brass substrate with the
photoresist patterns is then baked at 110.degree. C. for 20
minutes. After this hard baking, exposed brass regions are etched
by immersing the substrate in an etching solution containing ferric
chloride, FeC13. Typical time required to etch through the 10 mil
thick brass is about two minutes at room temperature. It is noted
that the etching time may be reduced by agitating the solution or
by increasing the solution temperature. It is further noted that
the final dimensions of each waveguide probe are determined firstly
by the dimensions of patterns in the photomask and secondly by the
etching of the brass substrate. Since the dimensions of each prior
art waveguide probes must be controlled precisely during the
mechanical machining, the time required is long and the fabrication
cost is high. FIG. 4(c) shows a cross-sectional view of the brass
substrate after the etching. For clarity, the fine brass wires and
fine photoresist patterns defining the fine brass wires (66, 66b')
given in FIG. 4(d) are not shown. After this, the remaining
photoresist patterns (69) and the photoresist (62) on the back
surfaces of the waveguide probes are removed by immersing the
substrate in acetone. This is followed by a rinse in de-ionized
water. FIG. 4(d) is a schematic top view of the waveguide probes
fabricated and before separation. It is noted that each L-shape
waveguide probe (40) is connected to adjacent waveguide probes by
fine brass wires (66, 66b'). A layer of gold is now plated over the
surfaces of each waveguide probe while all of the waveguide probes
are still connected together electrically. This is done by
attaching one part of the connected waveguide probes to the cathode
of an Au electrodeposition system (not shown) to deposit an Au
layer with a thickness of 1-5 micrometers. The purposes of the Au
layer are to increase the surface conductivity of the waveguide
probes and to facilitate the attachment to the pin. After the Au
deposition, the waveguide probes are rinsed in de-ionized water and
dried. The fine brass wires (66, 66b') connecting adjacent
waveguide probes are finally cut to isolate one waveguide probe
from the others.
[0033] During the etching of the exposed substrate regions to form
the L-shape waveguide probe, undercutting (U in FIG. 4(c)) is
unavoidable. In order to increase the reproducibility of
dimensions, it is preferred to reduce the amount of the
undercutting. One method to reduce the undercutting is to carry out
etching from both the front surface and the back surface of the
substrate (60). To achieve this, a second photomask (not shown) is
prepared to expose selectively the second photoresist layer (62).
Patterns on the second photomask are similar to those on the first
photomask, except that the ones on the second photomask are mirror
images of the second photomask. The alignment of the second
photomask against the substrate will be carried out in a special
mask aligner (not shown) which allows the precise alignment of
patterns on the second photomask to the patterns of the first
photoresist layer created by the first photomask. Hence, after
development, the patterns (not shown) on the back surface aligned
precisely to the patterns (64, 65) on the front surface. The
alignment of the patterns on the second photomask may be carried
out after the patterns of the first photoresist layer have been
developed. After the exposure of the second photoresist layer to
the ultraviolet light through the second photomask, the second
photoresist is developed and baked. Etching can now be proceeded
from both sides in order to reduce the undercutting. Since the
etching time required for the etching from both the front surface
and back surface of the substrate is about half of that required
from the front surface alone, the undercutting will be about half
of the undercutting (U) in FIG. 4(c).
[0034] Using the micro lithography and etching processes, in
addition good reproducibility of dimensions, non-symmetrical
waveguide probes with different dimensions for different frequency
ranges can be fabricated in the same fabrication run. After the
fabrication, the electrodeposition of the Au or Ag can be performed
simultaneously layers to reduce the surface resistance. The micro
lithography and etching method is particularly suitable for the
fabrication of non-symmetrical waveguide probes, which are
relatively difficult to manufacture using mechanical machining
methods.
[0035] As stated before, the selection of dimensions of the
waveguide probe will be made on the basis of the frequency range of
operation. Some examples of the dimensions of the non-symmetrical
waveguide probes for applications at different frequency ranges are
provided here. It is noted that these values are provided as
examples and in no way should be considered as limitations to this
invention.
1TABLE Some dimension examples of the non-symmetrical conductive
waveguide probes for operation at different frequency ranges
Frequency A B C D E F T Range (GHz) (mil) (mil) (mil) (mil) (mil)
(mil) (mil) 18-26 40 125 30 125 10 30 10 26-40 30 90 30 90 10 30 10
40-60 30 70 30 70 10 30 10 50-75 20 46 20 46 10 30 10 Here A and B
are the width (41c in FIG. 2) and length (41b) of the first arm
respectively, C and D are the width (42c) and length (42b) of the
second arm, E and F are the width (45) and depth (46) of the slot
and T is the thickness of the L-shape probe.
[0036] According to a third embodiment, a non-symmetrical waveguide
probe is attached precisely to the end portion of the pin to form
an MMIC/waveguide transition. The precision and reproducibility of
alignment are achieved using a novel alignment tool. Refer now to
FIG. 5, where there is shown a partial view of the alignment tool
(80), main parts of the alignment tool include a platform (81) to
receive the housing (20) and a recessed cavity (82) to accommodate
a non-symmetrical waveguide probe (40). This recessed cavity is
precisely machined so that when the waveguide probe is placed in
it, the slot (44) is facing the major exterior wall (28a) of the
universal conductive housing and the outer edge (83) of the second
arm of the waveguide probe opposing the slot is aligned to and in
contact with the wall of recessed cavity facing the pin. The
protruding end (7) of the first part of the pin is aligned to the
slot (44) of the waveguide probe. The alignment tool (80) is made
of metals such as Al in order to prevent solder from sticking
thereto during subsequent soldering process. The alignment tool is
designed and manufactured such that when the universal conductive
housing (20) is inserted with the attached pin facing the precision
slot into said recessed cavity (82), the pin (7) is automatically
aligned with the slot (44) of the waveguide probe. Fine adjustment
can now be made under an optical microscope (not shown) to obtain
the final precise position of the L-shape waveguide probe (40)
relative to the end (7) of the pin. Using this alignment tool, the
distance (84) between the outer edge (83) of the waveguide probe
and the major exterior wall (28a) of the universal housing is
determined by the depth of the recessed cavity. Since the length of
the first part of the pin extending beyond the major exterior wall
is known, the final position of the waveguide probe can be
precisely adjusted and controlled using this tool. It is also noted
that during the design of the non-symmetrical waveguide probes and
the alignment jig, the distance (88) between the major exterior
wall (28a) and the leading edge of the waveguide probe (40) should
not be too small in order to avoid shorting and poor impedance
matching. In addition, an electrical contact hole (87) is provided
to the alignment tool to facilitate micro soldering or welding of
the waveguide probe.
[0037] After the final positional adjustment, a small preform
(about 20 mils.times.20 mils.times.10 mils) of solder (86), such as
an alloy containing 60% Sn and 40% Pb having a melting point of
183.degree. C., is placed in a location near or on part of the gap
formed between the pin and the slot of waveguide probe. The
alignment tool is connected through an electrical contact hole (87)
to the ground of a micro welding/soldering machine (not shown). The
other electrical end of the micro welding/soldering machine is
connected to a fine tungsten probe (85). To weld/solder the
non-symmetrical waveguide probe (40) to the end of pin (7), a
voltage is switched on and set to a predetermined value. The fine
tungsten probe is then brought into contact with the pin. An
electrical current (I) is passed through the pin and the universal
housing, to generate heat in the region near the tip of the
tungsten probe and the pin, causing the preform of the solder (86)
to melt. Immediately after the melting, the melted solder flows and
fills the gap formed between the pin and the slot of waveguide
probe, the power to the micro welding machine is switched off to
let heat dissipate and the solder solidify. The waveguide probe is
now firmly and precisely attached to the pin. The housing with the
attached waveguide probe may now be removed from the alignment
tool. It is noted that during the waveguide probe attachment
operation, the housing (20) may be turned by 90 degrees around the
pin to a new position so that a waveguide section may be easily
mounted to the housing to form a module. In this case, a new
precision jig with a platform (81) of different vertical level is
used.
[0038] Since the non-symmetrical L-shape waveguide probes are
manufactured by the micro lithography and etching method, the
dimensional uniformity and reproducibility can be improved compared
to those for the prior art symmetrical plate-shape, cylindrical or
conical waveguide probes. Furthermore, using the alignment tool to
align and attach the non-symmetrical waveguide probe to the end of
the pin, the reproducibility of positioning can be easily achieved.
After the L-shape waveguide probe has been attached to the end
portion of the pin, as shown in FIG. 3(a), a universal launcher
adapter (51) is aligned and mounted to the conductive housing (20).
A conventional waveguide section (50) is then mounted to the
universal launcher adapter. Hence, after the mounting of the
universal launcher adapter and the waveguide section, the L-shape
waveguide probe is automatically aligned and located substantially
at the center of the cross section of the waveguide section and
universal launcher adapter, with the major broad surface (49) of
L-shape waveguide probe aligned to be substantially perpendicular
to the surface the major wall (28). A rectangular portion of the
major exterior wall (28a) defined by the through channel (52) of
the universal launcher adapter forms the short circuit end wall of
the combination of the universal launcher adapter and the waveguide
section. The L-shape waveguide probe is arranged so that the long
axis of the second arm is located at a quarter wavelength distance
from the short circuit end wall.
[0039] It is now clear that with this arrangement, the electric
field polarization of the excited microwave signals by the L-shape
plate waveguide probe can be controlled. Furthermore, the bandwidth
of operating frequencies may be improved by designing dimensions of
the L-shape waveguide probe. Compared to the prior art symmetrical
cylindrical or conical launching beads, or the symmetrical
waveguide probe fabricated by the micro lithography and etching
method, the performance of the non-symmetrical L-shape waveguide
probe has been improved.
[0040] While the invention has been described in conjunction with
illustrated embodiments, it will be understood that it is not
intended to limit the invention to such embodiments. For instance,
the L-shape waveguide probe may be fabricated using thin conductive
wires. The thickness of the waveguide probes may be different from
the one used in the examples, as long as they are thick enough so
that the mechanical strength is sufficient to prevent deformation
and vibration during operation.
* * * * *